It is usual in microscopy to bring the specimen, or the region of the specimen that is to be sharply imaged, into the focal plane of an objective. To do so, the specimen (which is usually mounted on a specimen stage) or the objective is displaced along the optical axis. Many microscopes are equipped with objective turrets in which several different objectives can be kept on hand. Often the entire revolving turret is mounted displaceably for focusing. In order to allow automatic focusing, the various systems are equipped with motors for displacing the objective or turret, or the specimen stage.
Microscope objective positioning systems that are arranged between the objective turret and the objective are known. These microscope objective positioning systems make it possible to displace the objective in the direction of the optical axis relative to the turret. The company styled Physik Instrumente, for example, markets piezo-controlled systems of this kind.
German Application DE 43 23 721 A1 discloses a microscope objective that comprises at least one correction mount for compensating for different coverslip thicknesses. The correction mount is axially displaceable and simultaneously rotatable about the optical axis of the objective. Jamming of the correction mount is thereby prevented.
German Application DE 37 35 324 discloses a microscope objective having a correction mount in particular for plane-parallel plates of different thicknesses in the specimen area, a front lens element and a rear lens group being arranged on the image side of a modifiable air gap. The correction mount is configured such that simultaneously with the modification of the air gap for aberration correction, an axial displacement of the entire optical system is performed in order to correct the location of the plane of focus.
German Application DE 31 05 018 A1 discloses an surgical microscope having an objective with two lens elements, whereby the back focus distance is changed by axially displacing one of the lens elements.
U.S. Pat. No. 4,796,974 discloses an apparatus for focusing electromagnetic waves. The apparatus contains a holder movable in three mutually perpendicular directions. Drive units for moving the holder in the three directions are provided. The apparatus can be used in a microscope and in a confocal scanning microscope.
In scanning microscopy, a specimen is illuminated with a light beam in order to observe the reflected or fluorescent light emitted by the specimen. The focus of an illuminating light beam is moved in a specimen plane by means of a controllable beam deflection device, generally by tilting two mirrors; the deflection axes are usually perpendicular to one another, so that one mirror deflects in the X direction and the other in the Y direction. Tilting of the mirrors is brought about, for example, by means of galvanometer positioning elements. The power level of the detected light coming from the specimen is measured as a function of the position of the scanning beam. The positioning elements are usually equipped with sensors to ascertain the present mirror position.
In confocal scanning microscopy specifically, a specimen is scanned in three dimensions with the focus of a light beam.
A confocal scanning microscope generally comprises a light source, a focusing optical system with which the light of the source is focused onto an aperture (called the “excitation pinhole”), a beam splitter, a beam deflection device for beam control, a microscope optical system, a detection pinhole, and the detectors for detecting the detected or fluorescent light. The illuminating light is coupled in via a beam splitter. The fluorescent or reflected light coming from the specimen travels back through the beam deflection device to the beam splitter, passes through it, and is then focused onto the detection pinhole behind which the detectors are located. Detected light that does not derive directly from the focus region takes a different light path and does not pass through the detection pinhole, so that a point datum is obtained which results, by sequential scanning of the specimen, in a three-dimensional image. A three-dimensional image is usually achieved by acquiring image data in layers, the track of the scanning light beam on or in the specimen ideally describing a meander (scanning one line in the X direction at a constant Y position, then stopping the X scan and slewing by Y displacement to the next line to be scanned, then scanning that line in the negative X direction at constant Y position, etc.). To allow image acquisition in layers, the specimen stage or the objective is displaced after a layer is scanned, and the next layer to be scanned is thus brought into the focal plane of the objective.
German Patent Application DE 196 50 392 A1 discloses a fine-focus stage for microscopes having a specimen plate, a retainer for the specimen plate, and an adjustment device that modifies the horizontal position of the specimen plate. In order to implement a parallel linear stroke of the specimen plate with a simple design, the fine-focus stage is configured in such a way that the retainer comprises a mounting region, preferably for attachment to a specimen stage or to the microscope, and a connecting region (5) toward the specimen plate; and that parallel arms articulated via bending points extend between the mounting region and the connecting region.
German Patent Application DE 199 24 709 A1 discloses an apparatus for fine positioning of a component, in particular for vertical fine positioning of an objective or an objective turret, having a lever arrangement and a drive system for the lever arrangement. The apparatus is characterized in that the lever arrangement acts directly on a rotary part; that the component is flexibly connected to the rotary part; and that the connection is implemented in the manner of a suspension system for the component that, upon rotation of the rotary part, modifies the position of the component by way of rolling contact of the flexible connection on the rotary part, thereby bringing about a linear motion of the component.
German Unexamined Application DE 44 40 758 A1 discloses an electromechanical positioning unit as an inertial drive for positioning specimens, having positioning precision down to the atomic scale and positioning travels up to the centimeter range. The positioning unit contains at least one preferably tubular piezoelectric actuator for transferring electrically controllable inertial motions to a rotor. The subject matter of the invention is a rotor that comprises at least one unit of greater mass (mass unit) and at least one flexibly bendable unit (bending unit), so that the magnitude of the frictional adhesion is adjustable by way of the bending unit(s) of the rotor, and the mass unit of the rotor ensures a high load-carrying capacity for the positioning unit. By means of this combination, the positioning unit can be used to position even heavier specimens, and the forces necessary for use as a tool can be exerted.
U.S. Pat. No. 5,682,076 discloses a piezoelectric micromotor for a disk drive.
The known systems for scanning a specimen along the optical axis and for focusing onto a specimen have the disadvantage that because of the large masses being moved, they are necessarily sluggish and slow. The apparatuses arranged between the turret and objective furthermore have the disadvantage that the optical path (tube length) is considerably lengthened.